Frédéric Colas

Method for small signal stability analysis of VSC-MTDC grids

This paper deals with small signal stability analysis of Voltage Source Converter based Multitermial HVDC grids (VSC-MTDC). First, a simplified model is used to predict the voltage dynamic behavior. Next, a modular method to build the state space model of the overall MTDC system is described. Model validation is achieved in time domain by a comparison with an electromagnetic simulation in EMTP-rv. As concrete example of effective application, a parametric study on the droop value is carried on a 3-terminal meshed HVDC grid. This example attests to the effect of the droop parameter on the stability of the overall system.

Real-time simulation: The missing link in the design process of advanced grid equipment

This paper describes a design process of advanced grid equipment including both dynamic simulations and power-hardware- in-the-loop. A case study concerning the insertion of an energy storage system in a large isolated grid is used as an illustrative example. First, the methodology developed to achieve a real-time simulation of the studied grid from its original dynamic model is presented. The real-time platform used within the framework of this project is based on the RT-LAB environment and is interfaced with real ultracapacitors through a power amplifier. Some experimental results are analyzed in the final part. The advantages of this methodology including power-hardware- in-the-loop are emphasized by illustrating its contribution to dynamic model validation and the obtained improvement in control system performances.

MMC Stored Energy Participation to the DC Bus Voltage Control in an HVDC Link

The modular multilevel converter (MMC) is becoming a promising converter technology for HVDC transmission systems. Contrary to the conventional two- or three-level VSC-HVDC links, no capacitors are connected directly on the dc bus in an MMC-HVDC link. Therefore, in such an HVDC link, the dc bus voltage may be much more volatile than in a conventional VSC-HVDC link. In this paper, a connection between the dc bus voltage level and the stored energy inside the MMC is proposed in order to greatly improve the dynamic behavior in case of transients. EMT simulation results illustrate this interesting property on an HVDC link study case.

Optimal control design for Modular Multilevel Converters operating on multi-terminal DC Grid

This paper proposes an advanced control strategy for Modular Multilevel Converters (MMC) integrated in Multiterminal DC grid. In this present work, a three terminal MMC-MTDC system connecting onshore AC systems with an offshore wind farm is setup. Firstly, the voltage droop control associated to the conventional cascaded controllers for MMC stations is studied, the dynamic behavior of the DC voltage is analyzed and some drawbacks are outlined. In order to improve the dynamic behavior of the controlled DC bus voltage and the stability of MTDC system, an optimal multivariable control strategy of each MMC converter is proposed and integrated in a voltage droop controller strategy. The designed advanced controller allows to improve the overall DC grid stability and to reach the droop values designed on static considerations with acceptable dynamic behavior. By means of numerical simulations in EMTP-RV software, it is shown that the proposed control strategy performs well the stability of MTDC grid with 400-level model for MMC compared with the classic existing control methods.

Power hardware in the loop simulation of wind farm contribution to grid frequency control

This paper aims to evaluate experimentally the capability of variable speed wind turbine to contribute to primary frequency control. Emphasis on isolated power system is performed by considering the French Guadeloupe island as a technical case study. The experimental work is based on the Power Hardware In the Loop (PHIL) method. A wind farm is emulated by equipments with reduced scale and is connected to a real-time simulator simulating the Guadeloupe power system via a reversible power amplifier. Two different scenarios have been tested. Comparison demonstrates that variable speed wind turbine can provide a significant support to primary frequency control.

Supervisory predictive control of a hybrid solar panels, microturbine and battery power generation plant

Abstract The main objective of this work is to design a supervisory predictive controller which optimizes the power flow of a renewable hybrid system (solar panels, microturbine and battery. Short time predictions of the solar power and the power reference will be embedded in the supervisor. Unlike expertise-based algorithms, the design of a generic and flexible strategy based on dynamic models is proposed. The performance index integrates the environmental impact, the cost of fuel, battery cycling and the energy delivery. Simulations and a real-time application in a Hardware-in-the-Loop plant are carried out to illustrate the applicability and effectiveness of the proposed supervisory predictive control design.

A vibration damping MPPT strategy for wind turbines using delayed feedback

Abstract At low speeds, wind energy conversion systems (WECS) can extract a maximum output power for a reference wind turbine-wind speed ratio. While the classical control strategy aims at tracking this Maximum Power Point using Power Signal Feedback, the transmission shaft flexibilities may yield undesirable mechanical vibrations. In this paper, a controller embedding a delayed power signal is proposed which is able to damp vibrations, when the time-delay is adequately chosen, while tracking the optimal set-point. Other strategies involving time-delayed feedback are proposed and simulations show the relevance of the proposed approach.

Improving robustness against grid stiffness, with internal control of an AC voltage-controlled VSC.

Voltage Source Converter-based transmission grids might be the future of power system with the increasing share of interfaced electricity generation. These systems should be able to support the utility grid autonomously. The present paper focuses on the VSC output filter design and internal control of filter states. Nested AC current and voltage loops are the state of the art for power converters, controlled as voltage sources, in Microgrid or UPS applications. These internal controls are candidates for future industrial implementation at high power level. However, in a VSC based transmission system, those controls will face various topologies while requiring robustness against transient events (load changes, line tripping, etc.). The following development aims at providing keys for designing a versatile internal control suitable for VSC-based transmission system.